1. Field of the Invention
The present invention relates to a vibration and sound isolation device (a vibration isolating and noise insulating device) for a cogeneration system with an engine, which prevents dissipation of vibrations and noise generated by the engine of the cogeneration system of a power (an electric power) generation system using heavy oil and others as fuels.
2. Description of the Prior Art
Fuels commonly used for engines include gasoline, light oil and heavy oil. Cogeneration systems employ a diesel engine operating on light oil as a fuel and often has a generator connected to the engine. If a low-quality fuel such as heavy oil can be used in the cogeneration systems, the fuel cost can be lowered and the fuel cost problem cleared. The cogeneration systems, however, have to deal with problems of environmental pollution, such as emission of exhaust gas, noise and vibrations, because they are often located in urban areas and fixedly installed at predetermined sites.
Japanese Utility Model Laid-Open No. 128150/1987 discloses an engine-driven heat storage apparatus equipped with a vibration isolation device. This engine-driven heat storage apparatus has an engine immersed in a heat medium such as water contained in a heat storage tank to store the waste heat of the engine in the heat medium. The engine is supported through a vibration isolation device on a support frame which is separate from the heat storage tank and made from a wire structural material.
Another waste heat utilization apparatus as a heat generating device with sound isolation is disclosed in Japanese Utility Model Laid-Open No. 4939/1990. This waste heat utilization apparatus has, for example, a construction in which a heat generating device such as an engine-driven generator that produces noise and heat during operation is installed in a housing to prevent dissipation of noise of the heat generating device and in which the waste heat of the heat generating device is used for heating water. In this waste heat utilization apparatus, the housing has a hermetically closed structure with its legs supporting the housing on the floor.
Further, Japanese Utility Model Laid-Open No. 166248/1989 discloses a sound isolation type water-cooled engine. The sound isolation type water-cooled engine has its engine body and muffler immersed in a sound isolation liquid filled in a sound isolation liquid tank and also has an air cleaner immersed in the sound isolation liquid with both its element replacement opening and air intake port exposed outside from the tank and with fins attached to the outer wall surface of a cleaner case.
Another vibration isolation structure for the cogeneration equipment is presented in Japanese Utility Model Laid-Open No. 114753/1990. This vibration isolation structure concerns a cogeneration equipment installation structure that integrates an engine and a generator as one system. In this structure, the engine body is immersed in water sealed in an enclosed case with the generator installed outside the enclosed case, and the engine and the generator are supported by a support means with a low spring constant, thereby suppressing vibrations transmitted from the engine to the outside.
The engines for cogeneration system and power supply system are fixedly installed and thus pose a serious problem of emission of noise, vibrations and exhaust gases from the engine. A possible measure of preventing emission of noise and vibrations from the cogeneration system may include installing the cogeneration system underground. This, however, is costly and has difficulty finding appropriate locations. Installing underground is therefore difficult in practice.
Vibrations and noise generated by engines present serious problems. When a large engine is mounted to a structure, its vibrations are transmitted to the whole structure, generating noise at locations where structure's frequency coincides with the frequency of the transmitted vibrations. Prevention of vibrations and noise is therefore very difficult. A common method of preventing vibrations and noise is to mount on a structure a base that comprises a rubber sheet put on the structure and a iron plate mounted on the rubber sheet, and to install the cogeneration system on the base.
The above noise and vibration prevention method, however, has a drawback that if the modulus of elasticity of the rubber is set small to absorb vibrations, the rubber will collapse too easily and if it is set large, not only will the rubber fail to absorb vibrations but also the engine may be dislocated, though over a small distance, by vibrations of the engine itself. When the engine is to be installed at a particular location in a building, as with an engine-driven power supply system, it is very difficult to suspend the engine and other equipment of the power supply system and install them on the base, which comprises a rubber and an iron plate on the rubber. Furthermore, installing the power supply system in a sound isolation case is equally difficult and costly, and thus impractical.
The problem of the fixed-location type engine in a cogeneration system is the magnitude of vibration-induced noise, which can hardly be reduced by ordinary noise insulating means. Vibration isolation effects may be produced by inserting an elastic member such as a rubber sheet between solid bodies. The rubber sheet, however, has a problem that if its modulus of elasticity is set large, the rubber will deform too easily and that if it is set small, noise will be transmitted. Hence, the sound isolation effect cannot be expected of the rubber sheet. The noise in the cogeneration system is produced as follows. Vibrations produced by the engine are transmitted to the structure at whose resonating points the vibrations are amplified to produce a resonating sound. Radiating sound generated by the engine is transformed into air vibrations that in turn cause resonance of solid bodies. Removing the radiating noise of the engine can be accomplished by arranging a vacuum chamber or an air chamber with small density in the noise radiation route.
As described above, when the engine of the power supply system is enclosed in a narrow space, sound waves, the cause of noise, are reflected by wall surfaces and the reflected sound waves are amplified by resonance, giving rise to a possibility of complex vibrations being generated. Hence, an effective way to cut off noise from the engine is to form the wall, through which sound waves are expected to pass, in a laminated structure in which a solid, a gas and a solid are stacked in that order; to cover the wall surface with a heavy material such as lead; or to form the wall in a laminated structure in which a space between the wall surfaces is evacuated to prevent propagation of sound waves.